Method of incorporating an amalgam or an amalgam-forming metal in a lowpressure mercury discharge lamp,and lamp produced by such method



Dec. 15, 1970 E. RASCH ETAL METHOD OF INCORPORATING AN AMALGAM OR ANAMALGAM-FORMING METAL IN A LOW-PRESSURE MERCURY DISCHARGE LAMP. AND

LAMP PRODUCED BY SUCH METHOD Filed May 6, 1968 FIG.2.

h S w R w 0 7- m W E N w m R D N E l S 6 d m0 H r E WITNESSES U.S. Cl.313-178 9 Claims ABSTRACT OF THE DISCLOSURE The mercury-vapor pressurewithin a low-pressure discharge lamp, such as a fluorescent lamp, isregulated by a thin layer of an amalgam-forming metal or amalgam that issprayed onto one of the lamp stems, preferably on the flared portionthereof, while the metal or amalgam is in a liquid state and before thestem is sealed into the envelope. The thickness of the metal or amalgamlayer is maintained below 100 microns, and preferably between 20 and 50microns, to provide a sufiicient amount of metal to properly regulatethe mercury vapor pressure during lamp operation and yet prevent themetal or amalgam from falling ofl the stem when the metal or amalgam isin a liquid state during the sealing-in of the stem and, in the case ofa fluorescent lamp of non-linear configuration, when the finished lampis heated and bent into the desired shape.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to mercury discharge lamps and has particular reference tofluorescent lamps and a method of incorporating an amalgam or anamalgam-forming metal within the lamp envelope at a location such thatit regulates the mercury vapor pressure and permits the lamp to beoperated at high power loadings and under high ambient temperatureconditions with improved eificiency and lumen output.

Description of the prior art As is well known, if a fluorescent lamp isoperated at higher than conventional power loadings or in enclosedlighting fixtures where high ambient tmeperatures are encountered, thelight output of the lamp decreases due to the excessive mercury vaporpressure generated within the lamp by the higher operating temperatures.This problem can be overcome by utilizing an amalgam which isstrategically located within the lamp so as to regulate the mercuryvapor pressure and permit the lamp to operate etficiently at such highpower loadings and high ambient temperatures. The amalgam must not onlybe placed at the proper location within the lamp but the amalgamcomposition and choice of the amalgam-forming metal or metals must besuch that the amalgam will function properly and provide the desireddegree of vapor pressure regulation. A fluorescent lamp having anamalgam that meets all of these requirements is disclosed in U.S. Pat.No. 3,007,071 issued Oct. 31, 1961 to A. Lompe et al.

The use of two sources of amalgam within a fluorescent lamp is alsoknown-one which heats up rather slowly when the lamp is energized andthen controls the mercury vapor pressure during operation, and asecondary source of amalgam which is located closer to the electrodesand thus heats up at a faster rate and provides a suflicient amount ofmercury vapor to enable the lamp to reach its rated output more rapidly.A fluorescent lamp of this United States Patent type is disclosed inU.S. Pat. No. 3,227,907 issued Jan. 4, 1966 to C. J. Bernier et al.

Various arrangements for retaining the amalgam at the desired locationwithin the lamp and for incorporating the amalgam or amalgam-formingmetal as an integral part of the lamp structure are also known. Forexample in German Pat. No. 1,104,060 an amalgam containing cadmium,indium, thallium, or tin, or alloys thereof, is applied to the innerwall of the lamp envelope in the form of a strip, a film or a bead. InGerman Pat. Nos. 1,l40,2861,l96,292 and 1,149,818, the amalgam-formingmetal is combined with a measured amount of mercury to provide thedesired amalgam composition which is then either pasted or rolled ontothe bulb wall, as, after being heated to at least partly soften it, isimpacted against the bulb wall and thus secured to a predetermined innerpart of the envelope.

However, if desired, only the amalgam-forming metal may be incorporatedinto the lamp initially and the amalgam subsequently formed when thelamp is dosed with mercury in the usual manner. In Japanese patentapplications 40-8518 and 40-2875 there are disclosed, for example,fluorescent lamps. in which a ring of indium is applied to the innersurface of the envelope at the middle of the lamp so that the indiumcombines with the mercury subsequently dosed into the lamp and forms thedesired indium-mercury amalgam composition, by an exterior heatingelement positioned around the middle of the lamp.

In German GM 1,934,678 there is disclosed a discharge lamp in which astrip of indium metal is attached to one of the stem presses. In GermanGM 1,937,402 there is disclosed another type of lamp in which indium isplaced in a sieve-like container that is pasted to the inner surface ofthe lamp envelope or attached to one of the lead-in wires by insulatormeans. In another type of fluorescent lamp a wire mesh holder isimpregnated with indium and then placed around one of the lamp stems. Afluorescent lamp having this type of pressure regulating assembly isdescribed in Illuminating Engineering, volume 60/1965, paper No. 9, p.534.

Experience has shown that optimum results will be achieved in amalgamtype lamps if the amalgam-forming metal or amalgam is in a form suchthat it extends over the greatest possible area. This makes itdifiicult, on the one hand, to apply the amalgam to such a large surfacewithin the lamp with sufficient adherence at a location where theamalgam will not block radiation, and, on the other hand, it complicatesthe manufacture of the lamp since portions of the lamp have to be cooledduring the exhaust and baking operations in order to prevent the amalgamfrom melting and flowing away from the desired location. In addition,while some amalgam-forming metals or amalgams are suitable as regardstheir ability to provide sufflcient mercury vapor pressure regulation,they have such a low melting point that they become liquid at theoperating temperatures within the lamp and thus create a situation wherethe amalgam may not remain at the desired location within the lamp.

OBJECTS AND SUMMARY OF THE INVENTION It is accordingly the generalobject of the present invention to provide an improved method ofincorporating an amalgam or an amalgam-forming metal within a mercurydischarge lamp which will avoid or overcome the aforementioned problemsassociated with the manufacture and use of lamps having this type ofmercury-vapor control means.

Another and more specific object is the provision of a method ofmanufacturing an amalgam-type fluorescent lamp which will permit theamalgam component to be 3 incorporated as an integral part of the lampstructure without disrupting the normal sequence of operation requiredto produce the lamp on a mass production basis.

Still another object is the provision of an amalgamcontainingfluorescent lamp that can be heated and reshaped after the lamp has beencompleted without dislodging the amalgam-forming metal from its properlocation within the lamp.

The aforementioned objects and other advantages are achieved inaccordance with the present invention by heating a suitableamalgam-forming metal, such as indium, until it becomes a liquid andthen spraying the metal, while in its liquid condition, onto one of theelectrode stems before it is sealed into the envelope. Theamalgamforming metal, or amalgam composition itself, is preferablysprayed onto the laterally protruding flared portion of the stem in sucha manner that a thin annular layer of metal or amalgam is deposited thatextends around the circumference of the flared portion of the stem.

The spraying time is controlled so that the metal layer a is very thinand has a thickness less than 100 microns, and preferably between 20 and50 microns. The partly metallized stem is sealed into the lamp envelopeand the other operations required to complete the lamp are carried outin the regular manner. While a suflicient amount of amalgam-formingmetal is contained in the layer to achieve the proper degree of vaporpressure regulation, the thickness of the layer is such that the metalremains in place even when it is in a liquid state during the sealinginof the stem.

The aforesaid properties and characteristics of the amalgam-formingmetal layer also permit the sealed-in lamp to be heated to the softeningpoint of the glass envelope and the latter to be bent into the desiredshape Without causing the liquid metal to fall off or run off the stem.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the inventionwill be obtained by referring to the accompanying drawing, where- FIG.-1 is a front elevational view of one end of an amalgam-containingfluorescent lamp which embodies the present invention, a portion of thelamp envelope being removed for illustrative purposes; and,

FIG. 2 is an elevational view on a reduced scale of a U-shaped amalgamtype fluorescent lamp that includes an amalgam-bearing stern of the typeshown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With specific reference now tothe drawings, in FIG. 1 there is shown one end of a fluorescent lamphaving a tubular vitreous envelope 11 which is hermetically sealed to avitreous stem 12 that is terminated at its outermost end by a laterallyextending flared portion 13 and at its innermost end by a press seal 14.The inner surface of the envelope 11 is coated with a suitableultravioletresponsive phosphor 15 in the usual manner and a pair oflead-in wires 16 are embedded in and extend through the press seal 14. Avitreous exhaust tube 17 is fused to the stem 12 in the region of thestem press 14 and communicates with the interior of the envelope 11through an aperture in the press in the usual manner to enable the lampto be evacuated, mercury dosed and charged with fill gas.

The inner ends of the lead-in wire 16 are attached to and support anelectrode coil 18 which is enclosed by an annular metal cap 19 of sheetiron that is supported in such position by a support Wire embedded inthe stem press 14. A strip v20 of a suitable amalgam-forming metal, suchas tin, indium and lead, is secured to the edge of the metal cap 19 toserve as an auxiliary source of amalgam and facilitate starting of thelamp.

In accordance with the present invention, the main mercury-vaporprQSSLll'Q QQ lLFOI means comprises an an- 4 nular band 22 of suitableamalgam-forming metal that is sprayed onto the flared portion 13 of thestem 12 in a manner such that it extends around the circumference of theflare at a region that is spaced inwardly from the rim of the flare thatis sealed to the envelope neck.

While the amalgam-forming metal layer 22 can be sprayed onto the flaredportion 13 of the stem 12 in various Ways, the stem 12 is preferablyrotated about its longitudinal axis and the liquid metal is sprayed ontothe flare by means of a nozzle that is inclined at an angle of aboutwith respect to the axis of rotation. The nozzle aperture and itsdistance from the stem are such that the annular strip of depositedmetal is of the desired width. The thickness of the metal layer iscontrolled by varying the time of spraying and, in the case of theembodiment here shown, a layer of indium about 30 microns thick wasspray-deposited in an annular strip such that the total quantity ofindium applied to the stem Was about milligrams. This provided anindium-mercury amalgam in the finished lamp which contained at leastindium.

The thickness of the layer 22 of amalgam-forming metal is critical inthat if it is too great the amalgamforming metal may drop off the stemdue to its own weight when the metal is in a liquid condition. This isavoided according to the invention by utilizing a thin layer, preferablyone having a thickness less than microns and preferably from 20 to 50microns. In the case of indium, a layer of this thickness enables themetal to adhere tightly to the flare by virtue of the high surfacetension, even when the indium becomes liquid during the sealing in ofthe stem 12. This is a great advantage insofar as stems with suchspray-deposited thin layers of amalgam-forming metals may be processedand sealed into the envelopes in the usual manner without anydetrimental aflects on the metal layer. Lamps utilizing such stems canalso be exhausted in the usual manner, and upon the dosing of therequired amount of mercury into the lamp, the desired amalgamcomposition is formed within the finished lamp.

The invention provides the additional advantage of permitting theamalgam to be applied to a large surface within the lamp at places whichare not located in the direction of radiation and which thus do notprevent light rays from leaving the envelope. Since the indium islocated at a region within the lamp which has a relatively highoperating temperature, a flatter light output versus temperature curveis achieved. Thus, compared to standard lamps the amalgam-containinglamp of this invention may be operated at high light output over aconsiderably broader range of ambient temperatures. At the most, thelight output of the amalgam lamp decreases by 10% over an ambienttemperature range of 25 C. to 75 C., with the maximum light outputoccurring at 45 C.

Another advantage of the invention is that a smaller quantity ofamalgam-forming metal is required compared to that required heretofore,as, for example, when the metal is placed within a wire mesh holder. Ithas been found that only one-third to one-fourth as much indium isrequired if it is sprayed onto the stem in accordance with the presentinvention. In addition, the method of the present invention eliminatesthe need for special stems or elongating the length of the stem and theneed for cool end chambers so that the shortening of the arc length anddarkened lamp ends produced by these structures are completelyeliminated.

Since special stems are no longer necessary and only small quantities ofamalgam-forming metal are required to achieve proper regulation of themercury vapor pressure, the present invention permits amalgam type lampsto be bent in any desired shape and thus permits the manufacture of lamptypes heretofore unavailable. Due to the fact that only a small quantityof amalgam-forming metal is used and it is sprayed onto the stem in avery thin layer, the metal does not drop off of the stem even when itbecomes liquid during the heating of the lamp envelope and themanipulation thereof required to bend it into the desired shape. Hence,high output fluorescent lamps and high ambient temperature lampscontaining amalgams can be made in shapes heretofore unavailable, as forexample, in the form of well-known circleline type and U-shaped lamps.

A U-shaped amalgam-containing fluorescent lamp a embodying the inventionis shown in FIG. 2. As shown, the envelope 11a is bent into the shape ofa U after the stems 12a have been sealed into the envelope and thefabrication of the lamp is completed. Suitable terminals 23 areconnected to the lead-in wires at each end of the lamp and the legs ofthe envelope are joined together by a suitable strap 23 to improve therigidity of the lamp. The use of an auxiliary source a of amalgam on themetal cap 19a in conjunction with the main reservoir of amalgam 22asprayed onto the stem flare is also advantageous in that it facilitateslamp starting.

A U-shaped lamp of the type shown in FIG. 2 manufactured in accordancewith the invention produces a light flux of 3300 lumens when operated ona line Voltage of 220 volts, at an ambient temperature of about 45 C.,and a power input of 65 watts. Its operating voltage was 85 volts itsoperating current was 885 milliamps. The efliciency of the lamp was,accordingly, in excess of 50 lumens per watt compared to an efficiencyof 43 lumens per watt and an output of 2800 lumens for conventionalU-shaped lamps of the same type.

It will be appreciated from the foregoing that the objects of theinvention have been achieved in that a very simple and convenient methodof incorporating an amalgam-forming metal or amalgam in a fluorescentlamp has been provided which permits the lamps to be manufactured with aminimum amount of amalgam-forming metal and in the usual mannerutilizing techniques and operations now employed in the mass productionof such lamps. In addition, a high output fluorescent lamp whichcontains an amalgam and is of nonlinear configuration has been providedwhich can be manufactured in the usual manner by heating the finishedlamp and bending the envelope into the desired shape.

While several embodiments have been illustrated and described, it willbe understood that various changes in both the method of manufacture andconstruction of the lamp may be made without departing from the spiritand scope of the invention.

We claim as our invention:

1. In the manufacture of a low-pressure mercury discharge lamp having avitreous stem at one end that is joined to the lamp envelope, the methodofincorporating an amalgam-forming metal as an integral part of the lampand at a location therein such that the metal will regulate themercury-vapor pressure when the lamp is operated, which methodcomprises;

heating the amalgam-forming metal until it is in the liquid state,

spraying the liquid metal onto a selected portion of the vitreous stemand depositing a thin layer of said metal thereon before said stem isjoined to the lamp envelope, and then joining said stem to the lampenvelope and completing the fabrication of the lamp.

2. The method of claim 1 wherein the spraying time is regulated so thatthe thickness of the formed metal layer is less than microns.

3. The method of claim 1 wherein:

said stem is terminated at one end by an outwardly flared portion, and

said amalgam-forming metal is spray-deposited on the flared portion ofsaid stem inwardly from the rim of said flared portion.

4. The method of claim 3 wherein said amalgam-forming metal is sprayedonto the flared portion of said stern while the stem is being rotatedabout its longitudinal axis so that the metal is deposited in a layer ofannular configuration that extends around the circumference of saidflared portion.

5. The method of claim 3 wherein the metal is sprayed onto the flaredportion of the stem until the thickness of the formed metal layer isbetween 20 and 50 microns.

6. In a low-pressure mercury vapor discharge lamp having a tubular glassenvelope which is hermetically closed by glass stems that are located atthe respective ends of said envelope and have outwardly flared portionsthat are sealed to the envelope, the improvement comprising a layer ofamalgam-forming metal that (a) is located on the flared portion of oneof said stems, (b) has a thickness less than 100 microns, and (c)contains a sufficient amount of said metal to regulate the mercury-vaporpressure within the lamp during the operation thereof.

7. The lamp of claim 6 wherein the thickness of said layer ofamalgam-forming metal is between 20 and 50 microns and said layerextends around the flared portion of said stem and is spaced inwardlyfrom the juncture thereof with said envelope.

8. The lamp of claim 6 wherein;

said envelope is of nonlinear configuration, and

said layer of amalgam-forming metal extends around the flared portion ofsaid stem and constitutes an annular strip that is spaced inwardly fromthe juncture between said flared portion and envelope.

9. In the manufacture of a low-pressure mercury discharge lamp having avitreous stem at one end that is joined to the lamp envelope, the methodof incorporating an amalgam composed of mercury and a selected metal asan integral part of the lamp and at a location therein such that theamalgam will regulate the mercury-vapor pressure when the lamp isoperated, which method comprises;

heating the amalgam until it is in the liquid state,

spraying the liquid amalgam onto a selected portion of the vitreous stemand depositing a thin layer of said amalgam thereon before said stem isjoined to the lamp envelope, and then joining said stem to the lampenvelope and completing the fabrication of the lamp.

References Cited UNITED STATES PATENTS 1,958,967 5/1934 Kniepen 313-178X3,287,587 11/1966 Menelly 313--178X 3,392,298 7/1968 Menelly 313-178XRAYMOND F. HOSSFELD, Primary Examiner US. Cl. X.R. 313174; 31625

